Doping of Graphene by Low-Energy Ion Beam Implantation: Structural, Electronic, and Transport Properties

We investigate the structural, electronic, and transport properties of substitutional defects in SiC-graphene by means of scanning tunneling microscopy and magnetotransport experiments. Using ion incorporation via ultralow energy ion implantation, the influence of different ion species (boron, nitrogen, and carbon) can directly be compared. While boron and nitrogen atoms lead to an effective doping of the graphene sheet and can reduce or raise the position of the Fermi level, respectively, ¹²C⁺ carbon ions are used to study possible defect creation by the bombardment. For low-temperature transport, the implantation leads to an increase in resistance and a decrease in mobility in contrast to undoped samples. For undoped samples, we observe in high magnetic fields a positive magnetoresistance that changes to negative for the doped samples, especially for ¹¹B⁺- and ¹²C⁺-ions. We conclude that the conductivity of the graphene sheet is lowered by impurity atoms and especially by lattice defects, because they result in weak localization effects at low temperatures

Jérémie 17,1-4TM, oracle contre ou sur Juda propre au texte long, annoncé en 11,7-8.13 et en 15,12-14

A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and <i>ab initio</i> calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N <i>K</i> and C <i>K</i> electron energy loss transitions show the presence of π* bonding states, which are highly localized around the N dopant. In contrast, the B <i>K</i> transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized π* states away from the B dopant. The asymmetry of the B <i>K</i> toward higher energies is attributed to highly localized σ* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations